Replacing adenoviral vector HVR1 with a malaria B cell epitope improves immunogenicity and circumvents preexisting immunity to adenovirus in mice
Takayuki Shiratsuchi, Urvashi Rai, Anja Krause, Stefan Worgall, Moriya Tsuji
Takayuki Shiratsuchi, Urvashi Rai, Anja Krause, Stefan Worgall, Moriya Tsuji
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Research Article Infectious disease

Replacing adenoviral vector HVR1 with a malaria B cell epitope improves immunogenicity and circumvents preexisting immunity to adenovirus in mice

Abstract

Although adenovirus (Ad) has been regarded as an excellent vaccine vector, there are 2 major drawbacks to using this platform: (a) Ad-based vaccines induce a relatively weak humoral response against encoded transgenes, and (b) preexisting immunity to Ad is highly prevalent among the general population. To overcome these obstacles, we constructed an Ad-based malaria vaccine by inserting a B cell epitope derived from a Plasmodium yoelii circumsporozoite (CS) protein (referred to as the PyCS-B epitope) into the capsid proteins of WT/CS-GFP, a recombinant Ad expressing P. yoelii CS protein and GFP as its transgene. Multiple vaccinations with the capsid-modified Ad induced a substantially increased level of protection against subsequent malaria challenge in mice when compared with that of unmodified WT/CS-GFP. Increased protection correlated with augmented antibody responses against the PyCS-B epitope expressed in the capsid. Furthermore, replacement of hypervariable region 1 (HVR1) of the Ad capsid proteins with the PyCS-B epitope circumvented neutralization of the modified Ad by preexisting Ad-specific antibody, both in vivo and in vitro. Importantly, the immunogenicity of the Ad-containing PyCS-B epitope in the HVR1 and a P. yoelii CS transgene was maintained. Overall, this study demonstrates that the HVR1-modifed Ad vastly improves upon Ad as a promising malaria vaccine platform candidate.

Authors

Takayuki Shiratsuchi, Urvashi Rai, Anja Krause, Stefan Worgall, Moriya Tsuji

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Figure 6

P. yoelii CS–specific immune responses and antimalarial protection after multiple immunizing doses of capsid-modified rAd.

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P. yoelii CS–specific immune responses and antimalarial protection afte...
(A) Immunization regimen. Groups of naive BALB/c mice were immunized intramuscularly with 1 × 108 v.p. of various rAds at week 0, 1 × 109 of various rAds at week 3, and 1 × 1010 of various rAds at week 6, and P. yoelii CS–specific humoral and cell-mediated immune response were measured at the time indicated. (B) Anti-(QGPGAP)3 and anti-(PPQQ)4 humoral responses. Antibody titers were determined by ELISA. Antibody titers below 100 were plotted as 50. Horizontal bars represent the geometric mean. (C) P. yoelii CS–specific CD8+ T cell response. P. yoelii CS–specific CD8+ T cell response in spleen was evaluated with IFN-γ ELISPOT assay at week 10. Data are shown as the number of IFN-γ–secreting P. yoelii CS–specific T cells in 1 million splenocytes. Horizontal bars represent the mean. (D) Antimalarial protection. The same groups of immunized mice in B were challenge with 2 × 104 infectious P. yoelii sporozoites via tail vein. Forty-two hours after the challenge, parasite burden in liver was determined by quantifying parasite ribosomal RNA with real-time PCR. For statistical analysis, the values were log-transformed, and then 1-way ANOVA followed by a Dunnett’s test was used. Horizontal bars represent the geometric mean. (E) Correlation between anti-QGPGAP antibody titer and parasite burden in liver. Log-transformed anti-(QGPGAP)3 antibody titer at week 10 and log-transformed parasite burden in liver in each mouse is scatter-plotted to evaluate the correlation between these variables. The solid lines show linear regression curves, and the dotted lines show 95% CI of the curves.